1. Field of the Invention
This invention relates to tape drive data storage systems. More particularly, the invention is directed to the modulation of tape tension during tape drive operations to facilitate data read/write accuracy.
2. Description of the Prior Art
By way of background, during operation in a tape drive data storage apparatus, a tape medium is transferred back and forth between supply and take-up reels while data is read from or written to tape by one or more read/write heads. Typically, the tape medium and the supply reel are mounted inside a tape cartridge that is inserted into a slot in the tape drive so that the tape is in magnetic contact with the read/write heads. The tape is advanced past the read/write head(s) by means of a pair of motors, one for each reel, which drive the reels at a desired tape speed.
For optimum data transfer through the read/write head(s), the tape must be precisely moved through the tape path and across the read/write heads. For best performance, the tension on the tape must be very accurately controlled because improper tape tension can lead to unreliable positioning of the tape relative to the read/write head(s), which can produce low readback signal amplitude and poor data transfer reliability. Improper tape tension can also cause poor stacking on the reels which can result in damaged media and therefore data loss.
In light of the foregoing, all modem tape drive data storage devices implement some form of global tape tension control. In some drives, this is done by controlling the torques on the motors that drive the supply and takeup reels. In particular, increasing the motor torques (which generally oppose one another) tends to increase tape tension, and visa versa. Another tension control method is to employ a capstan and pinch roller and then to use the reel closest to the head to tension to the tape. There are also various passive tape path components, such as grooved rollers and edge guides, but these do not allow tape tension to be directly controlled.
A disadvantage of the foregoing tape tension modulation techniques is that their response time is relatively slow, such that they are not capable of implementing rapid tape tension adjustments in response to high bandwidth transient tape tension variations, as are often seen during tape drive operation. Accordingly, it is desired to have an improved design for modulating tape tension in a tape drive data storage system. What is particularly needed is a tape tension modulation system that is responsive to high bandwidth tape tension transients that are not amenable to control using traditional global tape tension modulation techniques.